In oxidative phosphorylation during cellular respiration, what is the primary role of ATP synthase?

• A. It uses the proton motive force to catalyze $ADP+P_i\to ATP$.
• B. It pumps protons from the intermembrane space into the mitochondrial matrix using energy from ATP hydrolysis.
• C. It transfers electrons from $NADH$ directly to $O_2$ to form water.
• D. It synthesizes $NA{D}^{+}$ by oxidizing $NADH$ in the mitochondrial matrix.

Answer: (A)

Verified step by step guidance

1. Understand that ATP synthase is an enzyme complex located in the inner mitochondrial membrane that plays a crucial role in oxidative phosphorylation.
2. Recognize that during oxidative phosphorylation, a proton gradient (proton motive force) is established across the inner mitochondrial membrane by the electron transport chain pumping protons from the matrix to the intermembrane space.
3. Know that ATP synthase uses the energy stored in this proton gradient to drive the synthesis of ATP from ADP and inorganic phosphate (P_i). This process is called chemiosmosis.
4. Express the reaction catalyzed by ATP synthase as: \(\text{ADP} + \text{P}_{i} \rightarrow \text{ATP}\), where the enzyme harnesses the flow of protons back into the mitochondrial matrix to power this reaction.
5. Distinguish ATP synthase's role from other processes such as proton pumping (done by electron transport chain complexes), electron transfer to oxygen (complex IV), and NADH oxidation (complex I), which are separate steps in cellular respiration.